libnetfilter_queue: add license

pkgs/development/libraries/libnetfilter_queue/default.nix

···
   nativeBuildInputs = [ pkgconfig ];
   buildInputs = [ libmnl libnfnetlink ];
 
-  meta = {
+  meta = with stdenv.lib; {
     homepage = http://www.netfilter.org/projects/libnetfilter_queue/;
     description = "Userspace API to packets queued by the kernel packet filter";
-
-    platforms = stdenv.lib.platforms.linux;
+    license = licenses.gpl2;
+    platforms = platforms.linux;
   };
 }